DNA treasure trove

Consisting of over 60 different species, guenon monkeys are one of the most diverse groups of primates. Most are medium–sized with long tails, and many sport distinctive beards and whiskers. Their colourful facial patterns have prompted some to refer to guenons as birds among the primates.

Guenons belong to the tribe Cercopithecini and include vervet monkeys, red–tail monkeys and lesser spot-nosed monkeys. They split from the tribe Papionini – another primate group that includes baboons, macaques and mandrills – about 12 million years ago.

Previous studies into the guenon family tree have been hampered because it is hard to collect DNA samples from living monkeys. Some guenon species are kept in captivity, but many are endangered in their natural African forest habitat, making them hard to find and difficult to acquire permission to work with.

Now a team of researchers has overcome these obstacles by analysing DNA collected from monkey specimens held in museums.

The team was led by Professor Vincent Savolainen, from the Department of Life Sciences at Imperial College London. In a new study, published in Systematic Biology, they described how they used an advanced DNA sequencing technology to evaluate the evolutionary relationships within the guenon group.

Rather than collecting samples from live animals, Dr Katerina Guschanksi, the main author of the paper, extracted DNA from 120 museum specimens from four different museums: the Natural History Museum in London, Berlin’s Museum für Naturkunde, Belgium’s Royal Museum for Central Africa and the Royal Belgian Institute of Natural Sciences.

Professor Savolainen’s team was able to untangle a previously unsolved puzzle of when different guenon species evolved and how closely related they are to each other. They concluded that many new species of the monkeys evolved following changes in the African forest cover over the last 10 million years. They also provided the first evidence that some of the species could be the result of separate species interbreeding to produce hybrid species.

“These changes in forest cover isolated small groups of guenons in pockets of forest, where they eventually developed into separate species. In other cases, expansion of forests meant different species would be brought together and interbreed to create a new hybrid species,” he explained.

Dr Guschanski also used the data to identify when and where new species evolved and compared this to a timeline of climate changes in Africa. Professor Savolainen believes the research might help future conservation efforts.

“We learn from the past what might happen in the future to guenons and other monkeys as the size and shape of the planet’s forests change,” added Professor Savolainen. “It will certainly allow us to refine models of how animals disperse and potentially move into pockets of conserved forests, and possibly how they are going to respond to climate change.”

The ability to analyse DNA collected from museum specimens is relatively new science, known as ‘museomics’. The term was first coined in 2007, when Dr Stephan Schuster, a molecular biologist at Pennsylvania State University, reconstructed most of the woolly mammoth genome using hair samples that had been kept in a Russian museum for 200 years.

Since then, the genomes of a number of animals have been sequenced using museomics, including woolly rhinos, polar bears and Tasmanian devils.

Museomics owes much of its success to “next – generation” sequencing – the name given to a range of new DNA sequencing technology, able to analyse thousands of DNA sequences at once. According to Dr Schuster, the technology’s rate of development is actually outpacing Moore’s Law: the prediction that computing power doubles every two years.

As a result sequencing costs are dropping rapidly. Dr Schuster explains that sequencing the guenon monkeys might have cost around $36,000 a few years ago. Now it costs only a few hundred dollars.

“I think this study really demonstrates the power of museomics in mainstream genetic research,” said Dr Schuster.

Professor Savolainen’s team found that any part of the specimen could be used – whether skin, skeleton, skull or teeth – and that DNA sequences could be successfully collected from samples as small as 10 milligrams and from specimens up to 117 years old.

And Professor Savolainen believes museomics’ application goes much further. “We made the point that it will unlock museum collections so people could now sequence the whole of the tree of life just using the collection at the Natural History Museum,” he said.

A major advantage of sampling museum specimens is its ability to offer a snapshot through time of a species’ genetic diversity. Dr Schuster says that museomics enables the analysis of diversity either side of population bottlenecks, or just before species go extinct.

He also explains that breeding genetically diverse individuals is essential for conserving species. Museomics can help perform broad scans across species. In this way we can identify especially diverse populations and bring them together to improve the chances of species survival.